Tunable colour led module

ABSTRACT

A tunable colour LED module comprises at least two sub-modules, each comprising an LED, a wavelength converting element (WCE) and a reflector cup. The total light emitted by the module comprises light generated from each LED and WCE and the module is configured to emit a total light having a predefined colour chromaticity when activation properties of the LEDs are managed appropriately. The total light may have a broad white emission spectrum. The module combines the benefits of a low cost with uniform chromaticity properties in the far field, and offers long and controlled lifetime at the same time as flexibility and intelligence of tunable colour chromaticity, Colour Rendering Index (CRI) and intensity, either at manufacture or in an end user lighting application. A controlled LED module system comprises a control system for the managing activation properties of the LEDs in the sub-modules. Also described is a method of manufacture.

FIELD OF THE INVENTION

The present invention relates to a colour tunable light emitting diode(LED) module comprising multiple LED die and wavelength convertingelements, and in particular a method and device that eliminatesmanufacturer colour temperature binning by means of a designed colourmix trimming system.

BACKGROUND TO THE INVENTION

Light emitting devices and diodes are based on a forward biased p-njunction. LEDs have recently reached high brightness levels that haveallowed them to enter into new solid state lighting applications as wellas replacements for high brightness light sources such as light enginesfor projectors and automotive car headlights. These markets have alsobeen enabled by the economical gains achieved through the highefficiencies of LEDs, as well as reliability, long lifetime andenvironmental benefits. These gains have been partly achieved by use ofLEDs that are capable of being driven at high currents and hence producehigh luminous outputs while still maintaining high wall plugefficiencies.

Solid state lighting applications require that LEDs exceed efficienciescurrently achievable by incandescent and fluorescent lightingtechnologies. Currently one of the preferred routes for the generationof White light from an LED module is by use of a single colour LED (suchas a blue LED) and a wavelength converting element (such as a yellowphosphor). Wavelength converting elements (WCE) typically comprise of ayellow phosphor mixed in an encapsulant at the correct composition togenerate a white colour of the desired colour temperature. By modifyingthe fill fraction composition or % weight the white light colour may betuned. The ability to provide white light across a large chromaticityspace is advantageous for different lighting applications. However, dueto manufacturing inaccuracies associated with variation in LED emissionwavelength, LED emission bandwidth, variation in WCE % weight and WCEcomposition different LED modules will exhibit white light emissioncharacteristics with different chromaticity values. This is undesirableas sorting and binning of LED modules post manufacture is required.

In U.S. Pat. No. 6,788,011 the mixing of Red, 102, Green, 103, and Blue,104, primary colour semiconductor LEDs are employed to provide whitecolour light as shown in FIG. 1 a. In order to achieve the desired lightintensity as well as the colour chromaticity on a CIE diagram, a controlsystem is programmed with predefined LED driver power values for eachindividual LED colour. The light emission spectra intensity, 106,plotted against wavelength (as shown along 105) for each LED namely theRed LED, 109, Green, 108 and Blue, 107 are shown on the insert in FIG. 1a. The individual LEDs are assembled in a housing or board, 101. ThisLED lighting system suffers from several drawbacks.

Firstly, the LED lighting system proposed in U.S. Pat. No. 6,788,011suffers from poor Colour Rendering Index (CRI) typically around 27-30because of the individual narrow Red, Green and Blue wavelengths(approximately 10-25 nm bandwidth wavelength emission) having poorrepresentation of the complete visible spectrum of light which istypically experienced from incandescent bulb illumination or blackbodyradiation, 120, as shown in the insert in FIG. 1 a. As a reference theCRI for a blackbody radiation is 100 and the value ranging between 0 and100 defines how accurately light will portray colours relative to ablackbody source at the same nominal colour temperature.

Secondly, due to the different LED semiconductor material systemsrequired to generate Red (typically InGaAlP) and Blue or Green (InGaAlN)wavelengths the voltages, lifetime and junction temperature maydramatically vary from one LED to another adversely affecting thestability of the LED lighting system and the overall colour chromaticitywith lifetime as well as light intensity. This is typically verydifficult to monitor without the addition of feedback control systems.

In U.S. Pat. No. 7,213,940B1 another colour control system is proposed,whereby a first semiconductor LED with a first lumiphor is provided togenerate white light. In order to improve the CRI, a secondsemiconductor LED having a different emission wavelength is introducedinto the optical mixing. This system provides much improved ColourRendering Index (CRI) of around 80-92 due to the broader emissionachieved by the first LED and lumiphor. The introduction of the secondsemiconductor LED with Red emission wavelengths has a limited emissionbandwidth and hence is restricted in the amount that the CRI can beincreased. Secondly, the external efficiency of state of the artcommercial red emitting semiconductor materials such as InGaAlP istypically 30% which is much lower than that of GaN based blue emittingsemiconductor LED systems (state of the art commercial LED externalefficiency at 45%). Additionally, similar lifetime degradation problemscompared to LED lighting devices in U.S. Pat. No. 6,788,011 are alsoexperienced with the second semiconductor degrading at a different rateto the first LED.

In published U.S. Patent Application No. 2008/0048193 A1 a white LEDmodule including a further circuit board is described. The LED modulecross sectional schematic is shown in FIG. 1 c. In one example of theinvention a Green semiconductor LED, 103 and a Blue semiconductor LED,104 are placed on circuit board 101. A Red phosphor, 112, is disposedover 103 and 104 to provide a total emitted white light intensity, 106,against wavelength 105. The total emitted white light has a broad redphosphor emission, 109, and narrow blue, 107, as well as a narrow greenemission, 108, from the semiconductor LED die. The white light generatedfrom the LED module suffers from a poor CRI (expected to beapproximately 50-60) due to the narrow light emissions in the Blue andGreen wavelength regions. Additionally, the intensity of the Greenlight, 113, is dramatically attenuated, 108. The total green lightinitially emitted from the LED die 103 is shown as a dotted line, whilefollowing the propagation through the Red phosphor 112 the finaltransmitted green light is shown as the solid line 108. The attenuatedgreen light dramatically affects the total efficiency of the LED module.It is important to note that this applies across all wavelengths and notspecifically for Red phosphors only.

As will be appreciated by those skilled in the art, there is currently aneed for a LED module that combines the known benefits of low cost LEDmodules with the functionality of tunable colour chromaticity. It wouldbe desirable to provide a module having uniform chromaticity properties,and which also displays good CRI and intensity with a long lifetime.

SUMMARY OF INVENTION

According to a first aspect of the present invention, a LED modulecomprises a first and a second LED sub-module disposed on a high thermalconductivity sub-mount, wherein:

-   -   the first LED sub-module comprises:        -   a first semiconductor LED for generating light when            activated, the first LED being in thermal contact with the            sub-mount;        -   a first high thermal conductivity reflector cup, the first            LED being disposed in the first reflector cup; and,        -   a first wavelength converting element (WCE) at least            partially disposed over a surface of the first LED such that            light emitted from the first LED is incident on the first            WCE and is re-emitted at a substantially different            wavelength; and,    -   the second LED sub-module comprises:        -   a second semiconductor LED for generating light when            activated, the second LED being in thermal contact with the            sub-mount;        -   a second high thermal conductivity reflector cup, the second            LED being disposed in the second reflector cup; and,        -   a second wavelength converting element (WCE) at least            partially disposed over a surface of the second LED such            that light emitted from the second LED is incident on the            second WCE and is re-emitted at a substantially different            wavelength, the second WCE having different wavelength            converting properties to the first WCE;    -   wherein:    -   the first and the second semiconductor LED comprise the same        semiconductor material system;    -   the first WCE is at least partially in contact with the first        reflector cup and the second WCE is at least partially in        contact with the second reflector cup; and,    -   the total light emitted by the module comprises light generated        from the first LED and WCE and light generated from the second        LED and WCE, the module being configured to emit total light        having a predefined colour chromaticity when one or more        activation properties of the first and second LED are managed.

It is an object of the present invention that tight control of thecorrelated colour temperature (CCT) and Colour Rendering Index (CRI) ofthe total emitted light during manufacture is not required. It is afurther object of the present invention that the CCT and CRI of thetotal emitted light is defined using a control system post manufacturerather than by inspection and sorting of the LED module into differentCCT bins during module manufacture.

Typically, the LEDs are at least partially in direct physical contactwith the high thermal conductivity sub-mount for the efficientdissipation of heat. The reflector cups sit around the respective LEDand are designed to thermally dissipate heat generated by the respectiveWCE.

It is preferred that the first and/or second WCE is selected from agroup of WCE elements which comprises phosphors, quantum dots (QDs),organic light emitting material, and electrically, ionically- oroptically-pumped light emitting materials.

Preferably, the sub-mount comprises an electrical board havingelectrical tracking and an electrical isolation layer disposed betweenthe tracking and the substrate of the sub-mount. The substrate maycomprise of materials selected from a group of high thermal conductivitymaterials such as Cu, Al, W, Ag, CVD diamond, Diamond-Like Carbon (DLC)or ceramics such as AlN.

In preferred embodiments of the present invention, the sub-mount and/orreflector cup comprise a material having a thermal conductivity greaterthan 50 W/mK.

Preferably, the second WCE is adapted to re-emit light with a redshifted wavelength emission spectrum as compared to the first WCE andwith an emission bandwidth greater than 40 nm.

In preferred embodiments of the present invention, the first and thesecond reflector cup enables the total emitted light to be morecollimated than a Lambertian source and to allow the light emitted fromthe first and second reflector cup to mix in the far field.

Preferably, the LED module further comprises a third LED sub-moduledisposed on the high thermal conductivity sub-mount, the third LEDsub-module comprising:

-   -   a third semiconductor LED for generating light when activated,        the third LED being in thermal contact with the sub-mount and        comprising the same semiconductor material system as the first        and the second semiconductor LED,    -   a third high thermal conductivity reflector cup, the third LED        being disposed in the third reflector cup; and,    -   a third wavelength converting element (WCE) at least partially        disposed on a surface of the third LED;    -   wherein, upon activation,    -   each of the first, the second and the third semiconductor LED        emit light in the blue wavelength range;    -   the first WCE is configured to re-emit substantially in the        yellow wavelength range;    -   the second WCE is configured to re-emit substantially in the red        wavelength range; and,    -   the third WCE is configured to re-emit substantially in the        green wavelength range,    -   wherein the total light emitted by the module further comprises        the light generated from the third LED and WCE and the module is        configured to emit total light having the predefined colour        chromaticity when one or more activation properties of the third        LED are also managed.

In a preferred embodiment the first, second or third semiconductor LEDmay comprise an array of multiple LED die.

Preferably, light generated by the first, second and third semiconductorLEDs and by the first, second and third WCEs is combined to form a totalemitted light having a broad white emission spectrum. The white lightemission is achieved by combining the correct proportion of light fromthe first, second and third LED sub-module using a control system.

In a first particular embodiment, the first LED sub-module is a whiteemission sub-module and comprises a blue semiconductor LED and a yellowphosphor or fluorophore. The second LED sub-module has a dominantemission wavelength in the Red-Orange and comprises a blue semiconductorLED and a Red-Orange phosphor or fluorophore. The third LED sub-modulehas a dominant emission wavelength in the Green and comprises a bluesemiconductor LED and a Green phosphor or fluorophore. The first, secondand third LED module may further comprise a blue optical bandstopfilter. The LED module is designed to enable total emitted light havinga white light emission with a tunable CCT of greater than 100K. Thewhite light emission is achieved by combining the correct proportion oflight from the first, second and third LED sub-module using a controlsystem.

In a second particular embodiment, the first LED sub-module is a whiteemission sub-module and comprises a blue semiconductor LED and a yellowphosphor or fluorophore. The second LED sub-module has a dominantwavelength in the Red-Orange emission and comprises a blue semiconductorLED and a Red-Orange phosphor or fluorophore. The third LED sub-modulehas a dominant emission wavelength in the Yellow and comprises a bluesemiconductor LED and a Yellow phosphor or fluorophore. The first,second and third LED module may further comprise a blue optical bandstopfilter. The LED module is designed to enable total emitted light havinga white light emission with a tunable CCT of greater than 100K. Thewhite light emission is achieved by combining the correct proportion oflight from the first, second and third LED sub-module using a controlsystem.

In a third particular embodiment, the first LED sub-module is a yellowemission LED sub-module comprising a blue semiconductor LED and a yellowphosphor or fluorophore. The second LED sub-module has a dominantemission wavelength in the Red-Orange and comprises a blue semiconductorLED and a Red-Orange phosphor or fluorophore. The third LED sub-modulehas a dominant emission wavelength in the blue and comprises a bluesemiconductor LED. The first, second and third LED module may furthercomprise a blue optical bandstop filter. The LED module is designed toenable the total emitted light to have a white light emission with atunable CCT of greater than 100K. The white light emission is achievedby combining the correct proportion of light from the first, second andthird LED sub-module using a control system.

In a fourth particular embodiment, the first LED sub-module is a yellowLED sub-module and comprises a blue semiconductor LED and a yellowphosphor or fluorophore. The second LED sub-module has a dominantemission wavelength in the Red-Orange and comprises a blue semiconductorLED and a Red-Orange phosphor or fluorophore. The third LED sub-modulehas a dominant emission wavelength between the green and blue andcomprises a blue semiconductor LED and a Green phosphor or fluorophore.The first, second and third LED module may further comprise a blueoptical bandstop filter. The LED module is designed to enable the totalemitted light to have a white light emission with a tunable CCT ofgreater than 100K. The white light emission is achieved by combining thecorrect proportion of light from the first, second and third LEDsub-module using a control system.

In some embodiments the first LED sub-module may further comprise anoptical filter. The optical filter is at least partially in the path ofthe light emitted by the first semiconductor LED and the light emittedby the first WCE. The optical filter may be disposed proximal to thefirst WCE and distal to the first semiconductor LED. In someembodiments, the optical filter may be disposed between the firstsemiconductor LED and the first WCE.

Likewise, in some embodiments, the second LED sub-module may furthercomprise an optical filter. This optical filter is at least partially inthe path of the light emitted by the second semiconductor LED and thelight emitted by the second WCE. The optical filter may be disposedproximal to the second WCE and distal to the second semiconductor LED.In some embodiments, the optical filter may be disposed between thesecond semiconductor LED and the second WCE.

In embodiments comprising a third LED sub-module, this third sub-modulemay further comprise an optical filter. This optical filter is at leastpartially in the path of the light emitted by the third semiconductorLED and the light emitted by the third WCE. The optical filter may bedisposed proximal to the third WCE and distal to the third semiconductorLED. In some embodiments, the optical filter may be disposed between thethird semiconductor LED and the third WCE.

In one preferred embodiment each of the first, second and third LEDsub-module comprises an optical filter. The optical filter is at leastpartially in the path of the light emitted by the first, second andthird semiconductor LED and the light emitted by the first, second andthird WCE. The optical filter may be disposed proximal to the WCE anddistal to the semiconductor LED residing in each LED sub-module. In someembodiments, the optical filter may be disposed between thesemiconductor LED and the WCE residing in each LED sub-module.

Suitable optical filters may be selected from a group of optical filtersincluding dichroic filters, multilayer stack filters, colour correctorfilter, colour absorbing filters, diffuser filters, dye based filters,pigment based filters, diffraction based filters and refraction basedfilters.

One or more of the optical filters may comprise a structure selectedfrom a group of such as a gel based layer, a multilayer stack disposedon a glass sheet, a multilayer stack on a polymer film, a stack disposeddirectly on the LED sub-mount or pigment in-filled glass or polymer.

Further LED sub-modules may be included in the overall LED module, eachhaving an LED emitting at other desirable wavelengths. If required, asuitable WCE element may be included in the further sub-modules.

In a preferred embodiment, the module further comprises a fourth LEDsub-module disposed on the high thermal conductivity sub-mount, thefourth LED sub-module comprising:

-   -   a fourth semiconductor LED for generating light when activated,        the fourth LED being in thermal contact with the sub-mount and        comprising the same semiconductor material system as the first,        the second and, if present, the third semiconductor LED; and,    -   a fourth high thermal conductivity reflector cup, the fourth LED        being disposed in the fourth reflector cup,    -   wherein, upon activation, the first, the second and, if present,        the third semiconductor LED emit light in the blue wavelength        range, and the fourth semiconductor LED emits light in the near        UV or red-shifted blue wavelength range substantially different        to the blue wavelength emitted by the first, the second and, if        present, the third semiconductor LED, and    -   wherein the total light emitted by the module further comprises        the light generated from the fourth LED and the module is        configured to emit total light having the predefined colour        chromaticity when one or more activation properties of the        fourth LED are also managed.

This embodiment provides for further control and tuning of thechromaticity of the total emitted light.

According to a second aspect of the present invention, a controlled LEDmodule system comprises:

-   -   an LED module according to the first aspect of the present        invention; and,    -   a control system for managing activation properties of the        semiconductor LEDs in the LED module when activated, the control        system being adapted to manage the activation properties to        achieve the predefined colour chromaticity for the total light        emitted by the LED module.

Preferably, the control system is further adapted to monitor electricaland thermal properties of the semiconductor LEDs in the module and toprovide feedback to modify activation properties of the semiconductorLEDs in order to achieve the predefined colour chromaticity for thetotal light emitted by the LED module.

Preferably, the controlled LED module system further comprises a lightsensor oriented to measure the colour chromaticity properties of atleast part of the total light emitted by the module, the control systembeing coupled to the light sensor and adapted to provide feedback tomodify activation properties of the semiconductor LEDs to achieve thepredefined colour chromaticity for the total light emitted by the LEDmodule.

The control system may further include an interface for connecting thecontrol system to external sources and receiving information from theexternal sources.

Preferably, the total emitted light approximately resides along thePlanckian locus on a colour chromaticity diagram and within achromaticity rectangle bounded by the CIE (x,y) coordinates(0.300,0.300) and (0.525, 0.450).

According to a third aspect of the present invention there is provided amethod of manufacturing the LED module of the first aspect or thecontrolled LED module system of the second aspect, the method comprisingthe steps of:

-   -   die attaching a first LED and second LED on a sub-mount;    -   affixing a first reflector cup around the first LED;    -   affixing a second reflector cup around the second LED;    -   depositing a first WCE element on at least a surface of the        first LED and residing inside the first reflector cup; and,    -   depositing a second WCE element on at least a surface of the        second LED and residing inside the second reflector cup.

Preferably, when manufacturing the controlled LED module system, themethod further comprises the steps of:

-   -   assembling a control system and interfacing it to the first and        second LED; and,    -   presetting parameters in the control system, whereby the control        system is adapted to manage the activation properties of the        semiconductor LEDs in the LED module to achieve the predefined        colour chromaticity for the total light emitted by the LED        module.

As will be appreciated by those skilled in the art, the presentinvention provides the benefits of a low cost LED module with uniformchromaticity properties in the far field and having long and controlledlifetime yet also offer the flexibility and intelligence of tunablecolour chromaticity, CRI and intensity either at manufacture or in theend user lighting application. As indicated above, the invention can beimplemented in a wide range of configurations and various embellishmentsof the invention are possible, many of which are described below withreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present invention will now be described in detail withreference to the accompanying drawings, in which:

FIG. 1 a (prior art) shows a first known LED module;

FIG. 1 b (prior art) shows a second known LED module;

FIG. 1 c (prior art) shows a third known LED module;

FIG. 1 d (prior art) shows a known LED module;

FIG. 2 a shows a schematic cross section of an example LED module of thepresent invention;

FIG. 2 b shows a schematic top view of an example LED module of thepresent invention;

FIG. 3 a shows a schematic cross section of an example LED module of thepresent invention having associated far field emission profiles;

FIG. 3 b shows a graph of correlated colour temperature (CCT) againstfar field angle;

FIG. 4 shows a schematic cross section of an example LED module of thepresent invention with enhanced thermal dissipation aided by thesub-mount and reflector cup;

FIG. 5 shows a schematic cross section of another example LED module ofthe present invention;

FIG. 6 a shows a schematic diagram of an example LED module and controlsystem of the present invention;

FIG. 6 b shows a schematic diagram of another example LED module andcontrol system of the present invention;

FIG. 6 c shows a schematic diagram of another example LED module andcontrol system of the present invention;

FIG. 6 d shows a schematic diagram of another example LED module andcontrol system of the present invention;

FIG. 6 e shows a schematic diagram of another example LED module andcontrol system of the present invention; and,

FIG. 7 shows a flow diagram of a method of manufacture of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a high wall plugefficiency low cost, low thermal resistance LED chip on board (COB)module and control system having a light output that is flexible andintelligent capable of tuning colour chromaticity, CRI and intensity.The tunability is defined by the control system and may be pre-setduring manufacture or actively defined or monitored in the end userlighting application.

The present invention can be incorporated using a light emitting device(LED) of any semiconductor material system such as, but not restrictedto, InGaN, InGaP, InGaAs, InP, or ZnO. However, for illustrativepurposes and as a preferred example, Blue wavelength InGaN semiconductorLED having a vertical contact pad structure (sometimes termed verticalLED structure, or thin GaN) will be described in the bulk of thedetailed description of the invention.

In the first aspect of the present invention an LED COB module isdevised, as shown in FIG. 2 a. The LED die, 104, are die bonded usingsoldering, epoxy or any other attach process onto an electrical circuitboard, 204. Preferably, the electrical board comprises an insulatedmetal substrate (IMS) board. The electrical board comprises anelectrical tracking layer (typically comprising a Cu alloy for improvedthermal and electrical properties), which is employed to supplyelectrical connection to the ohmic contacts of the LED die. Thep-contact of the LED die is attached to an electrical tracking layerthat also introduces a first layer of horizontal thermal spreading. Theboard also comprises an electrical insulating layer disposed between theelectrical tracking layer and a thermally conductive sub-mount orsubstrate layer.

An LED COB module provides many benefits, whereby the direct attach ofthe LED die to the electrical board or substrate layer removes manyinterface layers that provide undesirable thermal interfaces thussimplifying packaging and dramatically reducing manufacturing costs.

The LED module further comprises a thermally conductive reflector cupassembly system, 211, affixed to the submount and aligned so that theindividual LED die reside in separate reflector cups.

A wavelength converting element (WCE), 201 and 112 and 203, issubsequently disposed inside the reflector cups. This may comprise of aphosphor, QDs, organic light emitting material or other electrically,ionically or optically pumped light emitting material.

Each individual LED and associated wavelength converting elementresiding in a reflector cup is termed the LED sub-module, 212, 213 and214.

In the present invention, at least two LED sub-modules having differentWCE elements are employed. In the preferred example described in FIG. 2a three LED sub-modules are incorporated into the LED module. Each LEDsub-module comprises an identical semiconductor LED die, 104 and adifferent WCE element (namely 201, 112 and 203).

Firstly, a white LED sub-module, 213, comprising a blue semiconductorLED, 104 and yellow phosphor, 112, is employed to achieve substantiallywhite light emission. A high efficiency yellow phosphor is employedaimed at achieving a cool colour temperature ranging between 10,000K and5,500K when the blue LED optically pumps the phosphor. It is an objectof the white LED sub-module, 213, to achieve maximum luminous efficiencywith minimal concern about achieving a specific high CRI number or awell defined colour chromaticity on a CIE diagram. The characteristicwhite light emission intensity profile, 207, is plotted againstwavelength, 105. The yellow emission component, 111, typically having apeak wavelength ranging between 545 nm and 580 nm is superimposed on theblue wavelength emission 107. It is apparent from the peak widths of 107and 111 that to provide a broad white light emission simulating daylightthe broad phosphor emission of 111 is preferred.

In a preferred example the white LED sub-module emits light having acolour residing in a rectangle bounded by the CIE (x,y) (0.00,0.00) and(0.350,0.350) while having luminous efficiency at least greater than 100lm/W at 350 mA current drive for LED 104.

Secondly, a red LED sub-module, 212, is formed of a blue semiconductorLED, 104 and substantially red phosphor, 112, are employed to achievesubstantially red light emission. The red phosphor centre wavelengthemission, 109, may range between 580 nm and 670 nm as shown on 206. Itis also an object of the invention that the emission from 104 isdramatically decreased by improving 104 pump coupling efficiency to theRed phosphor, 201. This is experienced by having a drop in the peakemission of blue emission 107 on plot 206. This is desirable in order toavoid increased blue component dominance in the total emitted light of106 in FIG. 2 a.

Thirdly, a green LED sub-module, 214, is formed of a blue semiconductorLED, 104 and substantially green phosphor, 209, which are employed toachieve substantially green light emission. The green phosphor centrewavelength emission, 209, may range between 500 nm and 545 nm as shownon 208. It is also an object of the invention in the case of the greenLED sub-module that the emission from 104 is dramatically decreased byimproving 104 pump coupling efficiency to the green phosphor, 203. Thisalso is desirable in order to avoid the increased blue shift of theresulting total emitted light on the CIE diagram.

During operation the white LED sub-module and the red and green LEDsub-modules are all electrically driven and the total emitted light willcomprise a cool white light mixed with red and green light emissionforming a warmer white colour. The resulting light will shift the (x,y)colour coordinates towards the Red region of the CIE diagram if the Redsub-module intensity is increased while a predominant shift towards theGreen region of the CIE diagram is experienced if the Green LEDsub-module intensity is increased.

In practical terms, if the white light component is centred on(x=0.35,y=0.35), the relative shift in the x coordinate, Δx, is apositive finite number and the relative shift in the y coordinate, Δy,is a negative number if the red component is increased, while in thecase of the increasing the green component the Δx is a negative finitenumber and Δy is a positive number.

The spectrum of the total emitted light, solid line 210, from the LEDmodule is shown in the graph 106 in FIG. 2 a. The broad emission,typically greater than 40 nm and preferably greater than 50 nm, from theyellow, green and red phosphor are arranged to overlap and provide acontinuous summation of emitted light closely resembling 120 andproviding superior CRI. Preferably, the CRI is greater than 85, greaterthan 90, and greater than 92.

In a preferred aspect of the present invention the total emitted lightemitted is substantially white and approximately resides along thePlanckian locus on a colour chromaticity diagram and at least within achromaticity rectangle bounded by the CIE (x,y) coordinates(0.300,0.300) and (0.525, 0.450).

The plan view of an example LED module of the present invention is shownin FIG. 2 b. Multiple LED sub-modules are formed on a single submounthaving electrical tracking 204. The multiple reflector cups, 211, areformed from a single metal sheet having high thermal conductivity forimproved thermal dissipation from the LED die and WCE element. Forincreased power output and uniform white light generation 3 white LEDsub-modules, 213, as well as 2 green, 214, and 2 red, 212, LEDsub-modules are formed. Further holes are located, 215, and employed forphysical attach of the LED module to a luminaire or heat sink. Thelocation and size can vary depending on the application and the finalend product.

The LED die residing in each reflector cup may further comprise ofclusters or arrays of smaller multiple LED die or large single power LEDchips. An array of arbitrary shaped LED die may also be employed such asrectangular, square or polygonal shaped LED die. In a preferred examplethe LED power chip dimensions is 1 mm×1 mm, 1.5×1.5 mm, 2.2×2.2 mm.

Conventional LED modules having an LED die and WCE emit light in aLambertian profile, this is shown in FIG. 1 d. The far field profile ofa typical system is plotted as light intensity, 301, against angle, 302(as a polar plot) and has a full width half maximum (FWHM) of 120degrees as shown in the insert in FIG. 1 d. In such a typical white LEDmodule an LED die or cluster of dies are typically arranged in a compactarray with a phosphor disposed on the surface. The close proximity ofthe LEDs and the single phosphor composition residing on all the LEDsenables the LED module to emit as a single light source. This allows theLED module to exhibit uniform colour chromaticity versus far field anglein a Lambertian profile. The summation of light emanating fromindividual LED modules separated by a finite distance introduces largevariations in colour chromaticity versus emission angle. This isespecially true when the observation point is of the order of theseparation distance of the individual LED modules and when the LEDmodules emit light of different wavelengths.

In a preferred example of the present invention the LED module comprisesLED die residing in individual reflector cups with the WCE disposedinside the reflector cup as shown in FIG. 3 a. The clearance formedbetween the top surface of the WCE element and the top edge of thereflector cup, 303, enables light incident on the reflector cup from theWCE to be reflected and collimated.

The summation of light emanating from individual reflector cups in thefar field can typically cause variations in colour chromaticity versusfar field angle. FIG. 3 b shows the difference in corrected colourtemperature (CCT) of an LED module of the present invention as comparedwith an LED module of the prior art. The colour chromaticity variationin the far field is affected by two factors. The variations inwavelength spectra emitted from different reflector cups as well asseparation distance between different reflector cups. These two criteriaintroduce large variations in chromaticity in the far field especiallyat large far field angles (FIG. 3 b). The artefacts are reduced when theemission is more collimated than Lambertian. It is important to notethat the larger the separation between the LED die and WCE the highercollimation is needed to improve chromaticity.

The LED module chromaticity uniformity is also greatly improved as thedistance between the observer and the LED module is increased. In thecase of the prior art an RBG module, 311, having spacing of 9 mm betweeneach individual R, G and B LED die is analysed at an observationdistance of 100 mm away. Similarly, the CCT vs far field angle isanalysed for the LED module of the present invention, 310, with anidentical spacing to the prior art between the Blue, Red and Green LEDsub-modules. Inspecting the graph indicates the improvement in CCT, 304,against observer angle, 305, uniformity when increased collimation inthe total emitted light is introduced. It is important to note that, forcomparison purposes, the LED module of the present invention does notinclude a White LED sub-module.

The reflector cup properties allows for the ability to modify the farfield emission profile as well as improve collimation. The reflector cupsurface finish may be specular, multi-faceted, textured or diffuse. Thereflector cup cone angle, material reflectivity as well as surfacefinish are designed to provide a far field pattern more collimated thana Lambertian source as well as improve light extraction from the opticalcavity formed. The reflector cup vertical cross section profile maycomprise but not restricted to parabolic, spline curves or multiplestraight sections. The reflector cup horizontal cross section profilemay be composed but not restricted to hexagonal, polygonal, ellipticalor circular profiles. The reflector cup may also be composed of amultiple part reflector system, where for example a first partcomprising of a smaller reflector cup or light pipe propagates andguides light into a secondary reflector cup designed for improved lightcollimation.

In a preferred aspect of the invention, the sub-mount and reflector cupcomprise aluminium metal for improved thermal dissipation. Duringoperation, the high power densities injected into the LED generate heatat the LED junction. It is also important to note that due to the highlight output densities generated by the LED the WCE element alsogenerates heat due to photon absorption resulting in some phononvibrations and non-radiative recombinations in the host material. WCEelements are typically prone to thermal de-rating where an increase inthe temperature of the WCE element reduces the quantum efficiency of theWCE. If the heat is not efficiently dissipated from both the LED and WCEelement the efficiency of the LED and the WCE degrades as well as thelifetime of the semiconductor and WCE. Additionally, as the degradationin efficiency is not linear, drifts in colour may also be experienced.This is not desirable and hence it is an object of the present inventionthat a high thermal dissipation sub-mount, 204 and reflector cup, 205 isemployed as shown in FIG. 4. It is also an object of the presentinvention that the LED is in physical contact with the sub-mount formaximum thermal dissipation and at least part of the WCE element is incontact with the reflector cup as shown by the solid lines.

In a preferred aspect of the invention, the sub-mount and reflector cupcomprise a high thermal conductivity metal, metal alloy or ceramic suchas Al, Cu, W, Ag, AlN, Al₂O₃, Si or SiC as well as compounds includingChemical Vapour Deposited (CVD) diamond and Diamond like Carbon (DLC).

In another preferred embodiment of the present invention, the sub-mountand/or reflector cup comprise of a material having thermal conductivitygreater than 50 W/mK, preferably greater than 150 W/mK.

In yet another preferred aspect of the present invention a firstencapsulant layer, 401, is disposed between the WCE element and thesemiconductor LED to enable remote WCE operation. The encapsulantcomprises of an optically transparent, low thermal dissipation polymer,silicone, resin, plastic or inorganic high refractive index material.This allows for protection of the LED die from environmental factors,improved light extraction from the LED die, as well as for improvedthermal isolation between the WCE and the LED. The thermal interfacegenerated between the WCE and the LED enables the WCE to operate at amuch lower ambient temperature improving quantum efficiency and lifetimeof the WCE. The control of the thickness of the first encapsulant alsoallows for modification of the height of the WCE in the reflector cupand ultimately the collimation of the total emitted light.

In another aspect of the present invention, the addition of a furtherblue emission LED sub-module, 503, is included as shown in FIG. 5. Theadditional semiconductor LED preferably comprises of a blue emission,501, centered between the peak wavelength of 111 and the peak wavelengthof 107. This is designed to enable further improvements in the CRI toachieve values greater than 90 where the total emitted light, 502, isadapted to simulate a black body radiation. In a further aspect the LEDmodule may additionally further comprise of an LED sub-module containinga near UV LED die. Near UV LED emission typically range betweenapproximately 300 nm and 430 nm. The addition of near UV emission isadvantageous in applications where the wavelength spectrum of daylightis to be replicated such as for skin treatments, dental, wellbeing andhealth applications.

State of the art Red semiconductor LED wall plug efficiencies (WPE) areapproximately 27% to 30% depending on the wavelength. However, in oneembodiment of the present invention a Blue GaN based LED (havingexternal quantum efficiency of approximately 45%) with a Red WCE elementcomprising a material such as a Red QD or Red phosphor (havingconversion efficiency of approximately 85%) demonstrates a totalefficiency (WPE) greater than 38%. This amounts to greater than 26%improvement in overall efficiency of the lighting system. Thewavelength-converted Red light emission also comprises of a broaderemission spectrum (typically greater than 40 nm) improving the overlapof the emitted spectrum the Red LED sub-module.

It is a feature of the present invention that the individual WCEelements emitting at specific wavelength bands are separated inindividual reflector cups to further reduce the scattering exhibited bythe finite size of the WCE colloids or clusters. WCE are optimised togenerate optimal light at a specific wavelength emission band, part ofthe optimisation includes modification of the colloid or cluster sizesto reduce scattering effects experienced by the light propagatingthrough the WCE. However, this is typically performed to enhancetransmittance of light at the emission band of the WCE and due to Miescattering effects, and the transmittance cannot be optimised for otherwavelength ranges.

This is particularly relevant for WCE elements comprising of Quantumdots or nanocolloids where the size of the emitting particle is of theorder of wavelength of the emitted light. Hence, by disposing WCEelements with similar emission spectra in the same reflector cups thetotal emitted light efficiency is further enhanced. The WCE elements maycomprise of host materials formed of colloids, nanoshell, nanorice,nanocolumns or alternatively macroporous structures.

In a second aspect of the present invention the LED module may beprovided with a control system. The control system may contain amicrocontroller, an array of LED drivers, memory, and multiple input andoutput channels. The control system is employed to provide thesemiconductor LEDs with the desired current or voltage drive intensityto enable a pre-defined colour chromaticity from the LED module to beachieved.

In a preferred example the LED module is factory pre-set to a predefinedcolour chromaticity, CRI and light output for a given input power. TheLED module further comprises a control system. During manufacture, thecontrol system is trimmed while externally monitoring the total emittedlight colour chromaticity, total light output as well as the CRI for theLED module. Once the predetermined chromaticity characteristics areachieved in the LED module no additional trimming or modifications arerequired and the LED module is finalised.

An example of a simple control system is shown in FIG. 6 a. The controlsystem may comprise of an array of LED drivers for each of the Red LEDsub-module 212, the Green LED sub-module 214 and the White LEDsub-module 213, each having individual components that may be modified(by means of tuning or trimming a characteristic such as resistance orcapacitance), 605, to enable each driver to generate a different poweroutput. One example method of pre-setting the colour chromaticity of theLED module is by use of active laser resistor trimming while monitoringof the light output characteristics of the LED module. A trimmingresistor is connected to the feedback circuit of each red, 601, green602 and white 603, LED driver allowing individual control of theintensity of each wavelength spectrum.

In another preferred example of pre-setting the colour chromaticity, amicrocontroller, 611, is employed (as shown in FIG. 6 b) to control thedimming input, 610, of the LED drivers of each colour LED sub-module.Instead of active laser trimming of the resistor the microcontroller isprogrammed to include the exact dimming control signal to achieve thecorrect LED power intensity. An interface, 612, for factory pre-settingis also included.

In another embodiment of the controlled LED module system, the controlsystem may also include a feedback loop. The feedback signal is achievedby use of an optical colour sensor as shown in FIG. 6 c. A percentage ofthe total emitted light is allowed to incident the colour sensor, 621.The signal is fed back, 622, into the controller, 611. This data isprocessed with pre-calibrated algorithms embedded in the controllerallowing the LED module to be adjusted for any deviations or drifts incolour chromaticity. The dimming lines of the LED drivers, 610 areaccordingly adjusted by the controller. An interface, 620, is alsoprovided for factory calibration algorithm downloads.

The optical colour sensor may comprise of but not limited to a lightsensor that analyses a component of the spectral content of the totalemitted light, an array of photodiodes coupled to colour filters orgratings, CCD array, photodetector, bandpass filters or a spectrometer.

In a further aspect of the present invention the feedback signal isindirectly determined from secondary sensors. This is achieved by use ofa temperature, voltage and current sensor as shown in FIG. 6 d. Thesesensors monitor the individual LED die for changes in operatingtemperature, 635, voltage, 633, and current, 634, across the lifetimeand build a parameter database in the controller memory. The temperaturesensor may be externally attached to the submount on the electricalboard. The object of the present invention can only be achieved due tothe use of identical semiconductor LED die. During operation, thedatabase of the properties is stored and continually monitored in themicrocontroller which determines the degradation of the LED and WCE dueto lifetime and operating temperature and is achieved by comparison toreference databases stored in the microcontroller and the current forindividual LEDs is adjusted using dimming, 610, to indirectly correctthe colour chromaticity of the total emitted light. The interface, 636,is also provided for factory calibration algorithms and colour controls.

FIG. 6 e highlights a schematic of the LED module of the presentinvention with a control system further including temperature, voltageand current feedback. In the present example, multiple Red, Green andWhite LED sub-modules are connected in series with each LED driver. Thedashed lines on the schematic indicate digital lines while the solidlines indicate analogue electrical lines.

The LED module of the present invention provides benefits duringmanufacture, as it eliminates the necessity for wavelength binning ofLEDs and phosphors prior, as well as post incorporation into the LEDmodule. This dramatically reduces the cost of sorting LED die prior toLED module packaging as well as eliminates the necessity to match LEDdie to the correct phosphor composition with a matched absorptionspectrum.

Additionally, introducing individual LED and WCE elements havingdifferent wavelength emission spectra enables the modification ortrimming of individual spectra regions in order to select apre-determined colour chromaticity on the CIE diagram. The passivetrimming may be achieved by electrically activating individual LEDs atdifferent powers and pre-setting the power ratios between individual LEDand WCE elements. This enables a single LED module having multiple LEDand WCE elements to achieve any predefined colour chromaticity within aspecific triangle on the CIE diagram without the need for manufacture ofmany LED modules and having only a finite manufacture yield of achievingthe desired colour chromaticity bin.

The elimination of manufacture binning also enables reduced LED modulecosts as the exact number of LED modules may be manufactured and factorypreset rather than a much larger volume that is binned due tomanufacture variability.

The LED module of the present invention also provides benefits for theend user, whereby introducing a control module enables the LED module tomodify and shift colour chromaticity at the users input. Additionally,the ability to preset the LED modules during manufacture enablesdramatically reduced manufacture leadtime for custom colour LED modules.Finally, the ability to control and monitor the LED module colourcharacteristics guarantees that the LED module maintains identicalcolour chromaticity over the complete lifetime of the LED module.

In a third aspect of the present invention a method of manufacture ofthe present LED module and control system is proposed, as depicted inthe schematic diagram of FIG. 7.

The LED die are attached, 701, on a sub-mount having an electricalisolation layer and a tracking layer. The ohmic contacts of the LED aresubsequently wire bonded, 702, to the appropriate electrical trackinglines. The metal reflector cups are subsequently aligned to the LED dieand attached to the submount, 703. An encapsulant is dispensed into thereflector cups, 704, and designed to protect the LED die and wire bondsfrom the environment while also improving light extraction.

The WCE elements are pre-mixed to the right percentage weight into anencapsulant. The encapsulant may be organic, inorganic or hybridmaterial. The correct WCE element is depositing in the pre-designatedLED sub-module, 704. It is designed that the WCE is at least residing onthe top surface of the LED die and in contact with part of the reflectorcup edge. The deposition of WCE elements in each of the multiplereflector cups is repeated, 705, until all of the individual LEDsub-modules have been completed.

The WCE may be deposited using a technique such as, but not limited to,dispensing, dip coating, screen printing, ink jetting, spraying, plasmadeposition and sputtering.

The control system and interface electrical tracking is subsequentlyassembled 706. The LED module is activated and the light output ismonitored to generate the presetting calibration parameters, 707. Thepreset parameters are downloaded into the control unit via theinterface, 708.

1. A LED module comprising a first and a second LED sub-module disposedon a high thermal conductivity sub-mount, wherein: the first LEDsub-module comprises: a first semiconductor LED for generating lightwhen activated, the first LED being in thermal contact with thesub-mount; a first high thermal conductivity reflector cup, the firstLED being disposed in the first reflector cup; and, a first wavelengthconverting element (WCE) at least partially disposed over a surface ofthe first LED such that light emitted from the first LED is incident onthe first WCE and is re-emitted at a substantially different wavelength;and, the second LED sub-module comprises: a second semiconductor LED forgenerating light when activated, the second LED being in thermal contactwith the sub-mount; a second high thermal conductivity reflector cup,the second LED being disposed in the second reflector cup; and, a secondwavelength converting element (WCE) at least partially disposed over asurface of the second LED such that light emitted from the second LED isincident on the second WCE and is re-emitted at a substantiallydifferent wavelength, the second WCE having different wavelengthconverting properties to the first WCE, wherein: the first and thesecond semiconductor LED comprise the same semiconductor materialsystem; the first WCE is at least partially in contact with the firstreflector cup and the second WCE is at least partially in contact withthe second reflector cup; and, the total light emitted by the modulecomprises light generated from the first LED and WCE and light generatedfrom the second LED and WCE, the module being configured to emit totallight having a predefined colour chromaticity when one or moreactivation properties of the first and second LED are managed.
 2. A LEDmodule according to claim 1, wherein the first and/or second WCE isselected from a group of WCE elements which comprises phosphors, quantumdots (QDs), organic light emitting material, and electrically,ionically- or optically-pumped light emitting materials.
 3. A LED moduleaccording to claim 1, wherein the sub-mount comprises an electricalboard having electrical tracking and an electrical isolation layerdisposed between the tracking and a substrate.
 4. A LED module accordingto claim 1, wherein the sub-mount comprise a substrate formed from amaterial selected from the group of high thermal conductivity materialswhich includes Cu, Al, W, Ag, CVD diamond, Diamond-Like Carbon (DLC),and ceramics.
 5. A LED module according to claim 1, wherein at least oneof the sub-mount and the first reflector cup and the second reflectorcup comprises a material having a thermal conductivity greater than 50W/mK.
 6. A LED module according to claim 1, wherein the second WCE isadapted to re-emit light with a red shifted wavelength emission spectrumrelative to the first WCE and with an emission bandwidth greater than 40nm.
 7. A LED module according to claim 1, wherein upon activation: eachof the first and the second semiconductor LED emit light in the bluewavelength range; the first WCE is configured to re-emit substantiallyin the yellow wavelength range; and, the second WCE is configured tore-emit substantially in the red wavelength range.
 8. A LED moduleaccording to claim 1, wherein the first and the second reflector cup areconfigured such that light from the first and the second LEDsub-assembly mix in the far field and such that the total light emittedfrom the LED module is more collimated than from a Lambertian source. 9.A LED module according to claim 1, the module further comprising a thirdLED sub-module disposed on the high thermal conductivity sub-mount, thethird LED sub-module comprising: a third semiconductor LED forgenerating light when activated, the third LED being in thermal contactwith the sub-mount and comprising the same semiconductor material systemas the first and the second semiconductor LED, a third high thermalconductivity reflector cup, the third LED being disposed in the thirdreflector cup; and, a third wavelength converting element (WCE) at leastpartially disposed on a surface of the third LED, wherein uponactivation: each of the first, the second and the third semiconductorLED emit light in the blue wavelength range; the first WCE is configuredto re-emit substantially in the yellow wavelength range; the second WCEis configured to re-emit substantially in the red wavelength range; and,the third WCE is configured to re-emit substantially in the greenwavelength range, wherein the total light emitted by the module furthercomprises the light generated from the third LED and WCE and the moduleis configured to emit total light having the predefined colourchromaticity when one or more activation properties of the third LED arealso managed.
 10. A LED module according to claim 9, wherein one or moreof the first, the second and the third semiconductor LED comprises anarray of multiple LED die.
 11. A LED module according to claim 1, themodule further comprising a fourth LED sub-module disposed on the highthermal conductivity sub-mount, the fourth LED sub-module comprising: afourth semiconductor LED for generating light when activated, the fourthLED being in thermal contact with the sub-mount and comprising the samesemiconductor material system as the first, the second and, if present,the third semiconductor LED; and, a fourth high thermal conductivityreflector cup, the fourth LED being disposed in the fourth reflectorcup, wherein, upon activation, the first, the second and, if present,the third semiconductor LED emit light in the blue wavelength range, andthe fourth semiconductor LED emits light in the near UV or red-shiftedblue wavelength range substantially different to the blue wavelengthemitted by the first, the second and, if present, the thirdsemiconductor LED, and wherein the total light emitted by the modulefurther comprises the light generated from the fourth LED and the moduleis configured to emit total light having the predefined colourchromaticity when one or more activation properties of the fourth LEDare also managed.
 12. A controlled LED module system comprising: an LEDmodule according to claim 1; and, a control system for managingactivation properties of the semiconductor LEDs in the LED module whenactivated, the control system being adapted to manage the activationproperties to achieve the predefined colour chromaticity for the totallight emitted by the LED module.
 13. A system according to claim 12,wherein the control system is further adapted to monitor electrical andthermal properties of the semiconductor LEDs in the module and toprovide feedback to modify activation properties of the semiconductorLEDs in order to achieve the predefined colour chromaticity for thetotal light emitted by the LED module.
 14. A system according to claim12, the system further comprising a light sensor oriented to measure thecolour chromaticity properties of at least part of the total lightemitted by the module, the control system being coupled to the lightsensor and adapted to provide feedback to modify activation propertiesof the semiconductor LEDs to achieve the predefined colour chromaticityfor the total light emitted by the LED module.
 15. A system according toclaim 12, the system further comprising an interface for connecting thecontrol system to external sources and for receiving information fromthe external sources.
 16. A system according to claim 12, wherein thepredefined colour chromaticity is such that the total light emitted fromthe LED module resides along the Planckian locus on a colourchromaticity diagram and within a chromaticity rectangle bounded by theCIE (x,y) coordinates (0.300,0.300) and (0.525, 0.450).
 17. A method ofmanufacturing a LED module according to claim 1 or a controlled LEDmodule system according to claim 1, the method comprising the steps of:die attaching a first LED and a second LED on a sub-mount; affixing afirst reflector cup around the first LED; affixing a second reflectorcup around the second LED; depositing a first WCE element on at least asurface of the first LED and residing inside the first reflector cup;and, depositing a second WCE element on at least a surface of the secondLED and residing inside the second reflector cup.
 18. A method ofmanufacturing the controlled LED module system according to claim 17,the method further comprising the steps of: assembling a control systemand interfacing it to the first and second LED; and, presettingparameters in the control system, whereby the control system is adaptedto manage the activation properties of the semiconductor LEDs in the LEDmodule to achieve the predefined colour chromaticity for the total lightemitted by the LED module.